Trunking system



H. MLBASCOM. VTRUNKING SYSTEM. APPLICATION FILED ocr. 21, 1918. 1,363,219.

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Patented Dec. 28, 1920.

3 SHEliIT||i- I N V EN TOR. Hbmeom BY Z M, A TTORNEY H. M. BASCOM.

TRUNKING SYSTEM. APPLICATION FILED OCT. 21, i918- 1,363 ,21 9. Patented Dec. 28, 1920.

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A TTORNEY H. M. BASCOM. TRUNKING SYSTEM. APPLICATION men OCT. 21. 1918.

Patented Dec. 28, 1920.

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ATTORNEY UNITED STATES HENRY M. BASGOM, OF NEW YORK, N. Y.,

ASSIGNOR TO AMERICAN TELEPHONE AND TRUNKING SYSTEM.

Specification of Letters Patent.

Patented Dec. 28, 119241 Application filed October 21, 1918. Serial No. 258,961.

T 0 all whom a may concern:

Be it known that I, HENRY M. BASCOM, residing at New York, in the county of New York and State of New York, have invented certain Improvements in Trunking Systems. of which the following is a specification.

This invention relates to telephone systems and more particularly to trunking systems or systems in which calls are extended from one oifice over trunks to another otiice where the connection is completed by a so-called B 0 erator. l

eretofore, when it was necessary to extend a call over a trunk to another oflice, it has been the practice for the A operator to communicate the call over an order wire to ascertained the connection desired by the.

calling subscriber, plugs into the jack of any idle trunk of a group of trunks lead; ing to a B operators position. If the B operator is not engaged her telephone set is at once automatically connected to the selected trunk and a signal is actuated to indicate the trunk selected. The A operator may then communicate directly with the B operator over the trunk itself without the use of an order wire and if desiredthe calling subscriber may be temporarily excluded from the circuit by means of a splitting. key or the like. The B operator having been.

informed of the connection desired associ-' ates the trunk with the line of the called subscriber. If one or more A operators should plug into separate idle trunks while the B operators set is connected to another trunk, the circuit is so arranged that the B operators set will be connected to but one trunk at a time and as each trunk connection is completed her' set will be automatically connected in definite order to the waiting trunks. The circuit is also arranged so that as soon as a trunk is seized by an A operator a busy signal appears at each A operators position to indicate that the trunk is in use and this busy signal remains oper ated until the connection is taken down.

The invention may now he more fully understood from the following description, when read in connection with the accompanying drawings, Figures 1, 2, and 3 of which constitute circuit diagrams of three dliierent embodiments of the invention.

Referring to Fig. 1, two sets of apparatus located, respectively, at stations A and B are shown, the apparatus included within the dotted lines in the upper left hand corner of the diagram being located at station A and the remaining apparatus at station B. At station A one of a plurality of cord circuits Cis shown terminating in the usual plugs P and P whereby subscribers lines terminating at said station may be interconnected. The outgoing plug 1" of said cord circuit is also adapted to cooperate with any one of the jacks, such as J,, of a plurality of trunks, such as T which extend from station A to station B for the purpose of interconnecting subscribers whose lines terminate at station A with subscribers whose lines terminate at station B.

In order that the so-called A operator at station A may communicate with the calling subscriber, a listening key 1 is provided whereby the A operators telephone set may I be bridged across the cord circuit in the usual manner. In order that the A operator at station 'A may communicate with the socalled B operator at station B over the trunk, to the exclusion of the calling subscriber, when the cord circuit is connected with the trunk, a splitting key 2 and a transformer 3 are provided for the cord circuit, the contacts of the splitting key being so arranged that the outgoing end of the cord circuit is disconnected from the re- 3O is dee'nergized. The trunks are arranged in mainder of the cord circuit and is directly erators telephone set is automatically connected to the trunk with which the connection is made sothat the B operator may receive from, theA operator the number of the desired subscriber at station B. Inasmuch as a plurality of A operators may have simultaneously plugged intoa plurality of trunks leading to the B operators position, the apparatus at stationB is so arran ed that the B operators telephone set 'wil be connected to but one trunk at a time, and when the connection over that trunk is completed it will be automatically disconnected therefrom and automatically connected to the waiting trunks in a predetermined order.

This result is accomplished by providing each trunk, such as T with relays, such as E and F When the E relay of any trunk is operated, the B. operators set is automatically connected to the trunk over the contacts of said relay and the circuits of the E relays of other trunks are held open until the connection over the trunk is come pleted, whereupon the E relay of that trunk an endless chain with respect to the E and -Ft relays, so that when the F relay of a.

trunk is operated upon the connection of the B operators telephone set thereto, said relay is locked up, thereby shifting the circuit connections so that if calls are wait-- ing on a plurality of trunks the E relay of the first trunk next in order" to that of the trunk over which a connection was just established will be energizedto connect the B operators set to the trunk to which it corresponds. As each connection is completed the B operators set is then automatically connected to the next trunk in regular order of rotation. By means of this arrangement of the circuits, the order of rotation begins anew with the last'trunk over which the connection was established'each time a new call comes in, so that during periods of heavy traffic there is no tendency v to discriminate against the last trunk of a series Situations may arise during heavy traffic periods such that the A operator is unable to get into communication with the B op-' erator immediately, due to the fact that a number of calls are waiting upon trunks leading to the B operators position. Should the A operator in such a case restore her splitting key and proceed to answer other calls which may be coming in, the B operator upon being connected to the trunk seized by such an A operator may get no response to her request to know the desired number. In

'1 ,ses,21e

such a case, it is desirable that the B tor should be able to listen out from a given trunk at will and for this purpose a master listening out key 4 is provided, and each trunk is further provided with a relay, such as D individual thereto. Upon the actuation of the-master listening out key 4, the D relay corresponding to the trunk to which the B operators set is'at that moment connected will be energized and locked up, thereby disconnecting the B operators telephone set from the trunk and permitting it to be connected to the next waiting trunk in order. The circuit connections are so altered by this operation that the A operator may only procure the attention of the B operator by withdrawing the plug of her cord circuit from the jack of the trunk and again reinserting it to start the succession .erator is responding to a call of this character another A operator should make a connection to another trunk, the signal lamp associated with that trunk will glow steadily. Inaddition, a pilot lamp 6 is providedwhich also glows under these conditions to indicate to the B operator that another call LS waiting, While a busy tone is applied to the trunk to indicate to the A operator that the B operator is busy. hen the B o'pera- 'tor connects the trunk to a called subscribers line the lamp 5 is extinguished. Its circuit is so arranged, however, that when the connection is taken down by the A operator it is again caused to glow togive a disconnect signal to the B operator who thenw disconnects the trunkfrom the called subscribers line. Each trunk is further provided with a busysignal device, such as 7, at each A operators position at station A, thesebusy signaling devices being so'- arranged as to indicate that the trunk' is busy as soon as the A operator plugs into the trunk, and tocontinue this indication until the entire connection has been taken down. I

Furtherdetails of the apparatus. will now be clear from'a description of the operation,

which is as follows: Assuming that a call has come in over a subscribers line (not shown) terminating at the station A, the A operator inserts the plug P of the cord circuit-C in the jack of calling subscribers line and by throwing the listening. key 1 130,

I operators position at station E. A circuit' bridges her telephone set across the cord circuit to ascertain the number of the desired party, in the usual manner. Upon ascertaining that the number is that of a party whose line terminates at a station, such as station B, the operator inserts the plug P of the cord circuit into a jack, such as of an idle trunk T leading to a B is now closed from battery, through supervisory lamp 8, overthe sleeve contacts of e the plug and jack and through the windings of sleeve relay 9 to ground. The supervisory lamp 8 now glows and the relay 9 is front contacts prepares a circuit whereby the relay 11 is bridged across the trunk,

said circuit being held open, however, at

this time, at the right hand contacts of the relay 9.

When the plug P was inserted in thel jack J, a circuit was also completed over'" 'the talking conductors. of the cord cir cuit and the trunk through the right hand high resistance winding of the trunk relay 12. A circuit is. also completed for the low resistance left hand winding of the relay 12 in parallel with its high resistance winding, over the middle back contact of the relay,21 and the extreme left hand back contact-of relay 15. Relay 12 at its front contact completes a circuit from battery,

through the lamp 5, over the front contact of relay 12lower back contact of relay 21,

and through the two windings of relay 15 in series to ground, causingthe lamp 5 to glow steadily. The resistance in circuit with the supervisory relay 14', when the high resistance winding of the relay. 12 is shunted by its low resistance winding, is such that therelay 14: is energized to shunt the supervisory lamp 8, thereby e'xtinguish- I ing it. The supervisory relay'14 isat once deenergized, however, since the relay 15 at its extreme left hand contact opens the circuit of the low resistance winding of the relay 12 thereby increasing the resist- .ance in series with the relay 14; so that said relay is 'denergized'and again opens the shunt about the supervisory lamp 8 which continues to glow steadily.

Assuming that the operators set is not at this moment connected to' any trunk, relay 15 at its right hand front contact" completes a circuit from battery, over the ditions then existing.

left hand back contact of relay D through the windin of relay E and through the left han Winding of relay F to ground, over a circuit which depends upon the con- Assuming that no call had previously been answered and that the relay 16 is, therefore, denergized, the circuit to ground will continue from the left hand winding ofrelay F over the left hand back contact of said relay, over the. right hand back contact of relay E leftv hand back contact of relay F right hand" back contact of relay E left hand back contact of relay F and over the similar back contacts of other E and F relays (not shown), over the right hand back: contact of relay E and the left hand back contact of relay F corresponding to the last trunk of the series and thence to ground a over the left hand back contact of relay 16.

Relays E and F are energized over the .cir-

.cu-it above traced, the former operating to bridge the B operators set across the trunk by means of its extreme left hand front contacts. At its inner front contact relay E completes a short circuit about the high resistance windings of the relay 15, through an interrupter 17, thereby causing the lamp 5 to flicker or vary in brilliancyin a distinctive manner to indicate to the' B operator with which trunk her telephone set is connected. Relay F upon being ener ized-completes a locking circuit over its le t hand front contact, from battery, over the right hand front contact of relay 15, left hand back contact of relay D, through the windings of relay 111,, left hand winding and left hand front contact of relay F through the winding of the relay 18 to ground. Relay 18 in shifting its armature disconnects ground from the-conductor 19 and completes a circuit through a resistance 20,'for the relayv 16. Relay '16 uponbeing energized disconnects the ground normally connected to the series circuit over the back contacts of the E and F relays, and over its front contact alters the circuit so that the ground connection for E and F relays hereinafter energized must pass through the winding of the relay 18. Relay E atits right hand contact maintains the initial ener ization circuits of the E and F relays of all ofthe other trunks open, sov long as the relay E remains energized and the operators set remain s connected to the trunk ,T,. This'preventsthe possibility of the .B. operators set being simultaneously connected to more than one trunk. The B operator upon observing the flashing of the signal lamp 5 is informed that an A operator desires to communicates with her over thefltrunk-T The A operator at station A may now throw the splitting key 2,

thereby disconnectingthe talking conduc- "tors connected to the plug P from the remainder of the. cord circuits and connecting them to the primary windings of a transformer 3 associated with the A operators 5 set. The .A operator may now converse with the B operator over the trunk T to the .exclusion of the calling subscriber. The B .;;operator upon ascertaining the number of 'thedesired subscriber inserts the plug P into the jack of said subscriber, thereby completing a circuit for the relay 21 in serice with the lamp 5. Relay 2l at its ppper frontcontact-completes the talking strands of the: trunk, and at its middle contact opens the circuit of the low resistance winding of j the relayf12 which, however, had already 7 been opened at the left hand contact of the relay 15. At its lower front contact relay .21 completes afcircui't in shunt with the lamp 5 over the sleeve contactsv of the plug P and the correspondingjack, through the winding of the relay 21, over the front contact of the relay 12, lower front contact of relay '21, back contact of'tripping relay 22,

back contact of relay 23 and'through'the winding ofrelay 24 tobattery. This circuit through-the relay, 24 is of suflicientl low resistanceto extinguish the lamp 5. elay 1 24 is now energized and connects ringing current to the line of the. calling subscriber over its front contacts'and through the winding of the tripping'relay 22 in a well I understood manner. As soonas the called.

subscriber responds the tripping relay 22 5 is energized to open ashort circuit about the winding ofthe relay 23 which is thereby'energized to short circuit theringing relay 2 1 and to lock up a shunt for the lamp -5' through the winding of relay 23.v The re- 1 15 which is accordingly deenergized, there- 5 by disconnecting the operators set fromthe trunk at the middle contact of said relay. Relay 15 at its right hand contact opens the lockin circuit through the winding of the relay T1 and the left hand wind- 6 ing of the relay F thereby deenergizing the relay E, to further disconnect the B operators set from the trunk at the left hand contacts of said relay. It will be remembered that the locking circuit for the relays at E and F included the winding of the relay Relay 21 upon being energized, in closing.

This relay is also denergized at this time thereby completing a locking circuit through the right hand winding of the relay F from ground over the back contact of relay 18, conductor 19, right hand front contact and right hand Winding of relay F over the conductor 27 and through the windin of the relay 16 to battery. ,Relay F is su ciently slow in releasing its armature to permit of this circuit being closed before said relay is dee'nergized. Relay 16 also're mains energized and in fact this relay in the normal operation of the system is perinanently energized once the system is set into operation, either by a circuit over the front contact of the relay 18 or by a circuit in series with the right hand winding of some one of the F relays. The relay F remains energized until'a call comes in over some other trunk. The relay lti-was provided .for the purpose of obtaining an alternative ground connection for the initial energizing circuit of the E and'F relays, so that shouldthe F relay last locked up become deenergized, because of the accidental falling off of its armature, no false action will occur due to the opening "of the initial energizing circuit through the winding of the relay 18.

Assuming now that a call should come in over trunk T (not shown) a circuit would be completed over the left hand back contact of the relay 1),, through the. winding of the relay E through the left hand winding and left hand back contact of relay F over the right hand back contacts of succeeding E relays and left hand back contacts of succeeding F relays (not shown) over the right hand back contact of relay-E left hand back contact-of relay F front contact of relay 16, right hand back contact of relay E left hand front contact of relay F through the winding ofrelay 18- to ground.

Relays E and F and 18 are now energized, the former connecting the operators telephone set to the trunk T and the latter disconnecting ground from the right hand looking windingof the relay F which is thereby deenerglzed and connects ground to the winding of the relay16' which is maintained energized. As soon as the connection over the trunk T is completed by the B operator,

the'circuit through relay E left hand winding of relay F and winding of relay 18 is openedand relays E and 18 are deenergized, the former disconnecting the operators set and the latter at its back contact completing a locking circuit through the right hand winding of the relay F in series with the relay 16.

Let us now assume that while the B operator was disposing of the connection calls had come in upon trunks T T and T The circuits of the relays E E and E would beheld open at the right hand contact of the relay E so long as said relay is Relays E F and 18' are energized, the

latter opening a locking circuit of the relay F which'is now deenergized so that the re lay 18 is maintained energized by the look ing circuit over the left hand front contact of the relay F Th'e'circuits of the E and F relays corresponding to trunks T and T are opened at the right'hand' contact of the relay E before said relays become effec tive so that the relays E, and. F corresponding to the trunk T, which is next in order to the trunk T over which the last call was made, have preference over the relays of all other trunks. In a similar manner, as soon asthe-relay E is released the relayF will" be locked up through its right hand wind- T, and T trunk T will havepreference. This results in locking up relay F, as soon as the call coming in over trunk T is disposed of so that the trunk T has next preference. It will thus be seen that where'ai plurality of calls are simultaneously wait-' ing upon several trunks the'trunk nearest in regular order to that trunk with which the last callwas made will have preference over all other trunks and as the operators set is successively connected to the trunks a different order of rotation is established be ginning withthe trunk to which theoperators setis connected. I

Returning now .to the connection 'originally described with reference to the trunk T if, when the plug P was inserted in the jack J with the consequent energization of the relay 15, the operators set hadbeen connected to some other trunk so that the relays E and F could not be energized, a circuit would have been completed from battery, through one winding of the transformer 28, winding of relay 29, over the extreme left hand back contact of relay E middle front contact of relay 15, over the lower conduc tor of the talking circuit of the'trunk to ground. A busy tone would have been transmitted through'the transformer 28 and over the circuit just described to the"trunk,thereby indicating to the A operator that the B operator was at that moment engaged. The relay 29 would also have been energized to cause the pilot lamp 6 to'glow and the lamp 5 would have been steadily illuminated to inform the-B operator that a callawaits her upon another trunk.

-Should the A operator desire to attend to other calls which might be await ng her she could do so by restoring-the splitting key 2 ing and if calls are waiting on trunks T and throwing the listening key of another cord circuit. In this case when the B operators set is finally connected to the trunk T the B operator might be unable to secure any response. to her request for the number of the called subscriber. Should the-B operator desire to take up the next call awaitmg her upon a trunk, she could do so by throwing the master listening out key 4:,'

thereby completing a circuit from battery over-the back contact of relay 30, right hand contact of key 4, inner right hand back contact of relay D right hand winding and outer right hand back contact of said relay, right hand front contact of relay E and thence over the left hand front contact of relay F to ground through the winding ofrelay 18. Relay D is energized over the circuit above traced and at its left hand contact opens the circuit of the relay E and the lefthand winding of the relay F so that the relay E, is deenergized to disconnectthe B operators set from the trunk. The operators set is now free to be automatically connected to the next waiting trunk in regular order. The relay D at its left hand front contact is locked up through its left hand winding over the right hand front contact of relay 15. Relay D upon being energized, inclosing its right hand front contacts, completes a locking circuit which is maintained so long as the key a. is operated, as follows: from battery, over the left hand make con tact of key 4, inner right hand front contact of relay D right hand winding and extreme righthand front contact'of relay D throu h the winding of relay 30 to ground. elay 3O disconnects battery from the conductor 31 as soon as the relay D is energized to prevent the possibilityof the actuation of the D relay corresponding to the next trunkto which the 'operators set is connected, which might occur if the master listening out lon key'l was held operated too 'fhe relay D, now remains'locked up over its left hand windings so long as the plug P remains inserted in the ack J Shoul the A operator desire to again call the B operator she may do so by withdrawing the plug P from the jack J and again inserting it, as this action results in the momentary deenergization of the relay 15 which opens the locking circuit of relay D restoring the same to normal. The B operators set will now be connected to the trunk T in its regular order in a manner already described.

When the calling subscriber hangs up, the

supervisory relay 13 is deenergized, thereby causing the supervisory lamp 32 to glow. VVhen-the called subscriber hangs up, the relay 25 of the trunk is deenergized, thereby opening a shunt circuit through the low resistance winding of 'therelay 12 so that the .windings of the relay 12, however, and no circuit changes controlled by said relay take place. The resistance of relay 11 is suflic-iently high to denergize the relay 12, also, so that the shunt circuit which previously existed about the lamp 5 is opened at the right-hand contact of relay 12, thereby causing the lamp 5 to glow. The B operator upon observing the steady lighting of this lamp withdraws the plug P from the jack of the called line, thereby de'e'nergiz-ing the relays 21 and 23. Relay 21 upon being deenergized, at its middle back contact connects the low resistance winding of the relay 12 in shunt with the high resistance winding, thereby increasing the current flow through the windings of relay 11 sufficiently to energize said relay. Relay 11 at its con tact opens a circuit of the slow release relay 10 which in turn opens ,the circuit of the busy signals, such as 7, and disconnects the relay 11 from the trunk. The action of relays 10, 11 and 12, just described, is for the purpose of maintaining the busy signals,

I such as '7, of the trunk actuated,'-after the A through the winding of the relay 18.

operator has withdrawn the plug from the jack, so as'to indicate that the trunk is busy up to the moment that the B operator finally takes down the connection by withdrawing the plug P 7 Fig. 2 shows a somewhat modified form of circuit arrangement which differs from that of Fig. 1 mainly in that the relay 18 is V omitted and its function performed by the several F relays. It will be remembered that in the arrangement shown in Fig. 1 the relay 16 is at all times locked up in series with vthe right hand winding of some oneof the F relays so that the initial energizing circuit of the-E and F relays passes to ground The relay 16 was provided in order to obtain an alternative ground connection for the initial energizing circuit of the E and F relays in case the F relay last locked up should be dee'nergized due to the accidental falling off of its armature, thereby opening the initial energizing circuit through the winding of the relay 18. The relay 18 operatedto unlock the F relay corresponding to the trunk over which the last call was made each time a call is initiated on a new trunk. In the circuit arrangement of F ig.'2 the relay 16 was made.

performs the same functions as in the arrangement of Fig. 1, while the functions performed by the relay 18 are performed in Fig. 2 by the F relays. In order to secure this result the locking circuit through the right hand winding of each F relay passes in series through the contacts of all of the relays to the right of it so that the operation of initiation of a call on any of the trunks corresponding to said relaysunlocks the F relay previously locked up and locks up a new F relay. Furthermore, the F relay of the last trunk of the series which is the F relay shown at the extreme left in the diagram controls the locking circuit of all the other F relays so that a call coming in on the last trunk of the serieswill unlock any F relay previously locked up.

The operation of the circuit shown in Fig. 2 is similar to that already described in connection with the diagram of Fig. 1 up to the point where the relay 15 is operated in response to the insertion of the plug P in the jack J As soon as the relay 15 is energized a circuit is completed from battery, over the right hand front contact of said relay, left hand back contact of relay- D through the winding of relay E and the left hand winding of the relay F and thence to ground over "a circuit depending upon the trunk over which the last call If no call had been previously made the circuit would continue over the left hand back contact of the relay F right hand back contact of relay E left hand back contact of relay F and thence in series over the back contacts of all of the other E and F relays, including relays E and F to ground, over the back contact of relay 16. If, however, a call had previously been made over the trunk T the relay F would have been locked up in series with the relay 16 so that the circuit would have been extended from the left hand winding of the re lay F over the back left hand contact of said,

relay, back right hand contact of relay E andover the front left hand contact of relay F to ground. Relay E upon being energized shunts the high resistance winding of the relay 15 through the interrupter 17 and causes the signal lamp 5 to flash. Said relay also connects-the B 'operators telephone set over its left hand front conpleted for relay F from ground, over the right hand front contact of relay F extreme right hand back contact of relay F and through the winding of relay 16 to bat- A locking circuit is also com ter Assuming that the relay F, has been loo-lied up by a previous call the energizer.- tion of relay F, opens a locking circuit through the right hand winding of said relay F 2 by disconnecting the ground therefrom at the right hand contact of relay F If while the circuit arrangement is in the I condition just described a call should be ini-' and the locking circuit, through the winding of relay E and the left handwinding of relay F is opened. Relay E is de'e'ner- I gized and disconnects the B operators telephone set from the trunk T The relay F however, remains locked up through its right hand winding. '-As soon as the armature of the relay E falls o'fi' a circuit will be completed for the relays E and F through the winding of the relay E lefthand winding of relay F left hand back contact of relay F front contact of relay 16, right hand back contact of relay E and left hand front contact of relay F :to ground. The E and F relays of the trunks T and T will not beenergized as their circuits pass over the right hand' back contact of the relay E It will, therefore, be seen that the trunk T which is nearest the trunk in the endless chain over which the last call was extended receives preference- Relay F x at its left hand front contact locks up relays'E and F in series and at its right hand contact opens the lockin circuit through the right hand winding of which is accordingly denergized. The locking circuit is nowcompleted through the right hand winding of relay F from battery, winding of relay 16, righthand winding of relay F inner right hand front contact of said relay, back right hand contacts of all of the other F relays including. F F and F to ground. 1

' As soon as the call originating on trunk T has been completed relay E is dener Qgized, and assuming that calls are waiting on the trunks T T and T it will be seen that the trunk T, vill obtain preference over the other trunks. WVithout further tracing the operation 'of the circuits in detail it will be apparent that with regard to their E and F relays, the trunks are. arranged in an endless chain with the F relay corresponding to the trunk over which the last call was extended locked up so that a relay F plurality of calls simultaneously 0riginating on other trunks or awaiting the completion of the call on the last trunk will be taken u in regular: orderbeginning with the trun whose E and F relays are nearest to the right of the corresponding relays of the trunks on which the last call arose. The remaining features of the circuit arrangement are the same as those described in, connection with Fig. 1 and need not be further discussed.

A still further modification is illustrated in Fig. 3. In this figure the relay 16 per- "circuit of the F relays.

forms a function somewhat similanto that of the relay 18 of Fig. 1 in that it determines the opening and closin of the locking locking windings of the F relays are omitted with the result that the order of rotation of calls will always begin with the-trunk T instead of with the trunk over which the last call took place, providing there is an interval between the last previous-call and a plurality of simultaneous calls on other trunks. If, however, calls on aplurality of trunks are awaiting the completion of the last call, the order of rotation will begin with thetrunk upon which the last call ori imated. with the first calling trunk to t e right thereof obtaining preference.

The action just described will be apparent from a more detailed description of the operation. Assuming that a call has originated on the trunk T the relay 15 will be energized as already described 'in conneche right hand tion with previous figures, thereby completing a circuit through the windings of the relays E and F in series and thence to ground either over the back contact of the relay 16 or over the front contact of an F relay previously locked up through the winding of relay 16. The locking circuit is then'completed for the relays E and F over the front left hand contact of the relay F and through the winding of the relay 16 to ground. Relay E functions in exactly the same manner as the E relays of the cir- 'cuits previously described. 'As soon as the call has been extended to thecalled subscribers line relay 15 is deenergized and the locking circuit through the relays E F and 16 is opened and said relays are denergized.

If no'call should be waiting at this moment the circuit is restored to its normal condition and the next call arising on any trunk will close the circuit through the E and F relays of that trunk to groundover the back contact of the relay 16., If,1however, at the time the circuit through'the; relays E F and 16 was broken a call should have been waiting on some other trunk, as, for instanceth trunk Tgrelays E and F would have been I deenergized but a new circuit would have been completed for the relays E and F over the back left hand contact of relay F of rela back right hand contact of relay E back left hand contact of relay F front contact i sible because the F relays and the relay 16 are slow to release their armatures. Relay 16 will, therefore, remain energized and will be locked up in series w1th the relays E and F It will be seen, therefore,-

that a difference in operation results, depending on whether or not an interval elapse between calls. If the last call, for instance, should come in over the trunk'T and after an interval calls should arise simultaneously on trunks T and T the relay '16 would have been denergized in the meantime so that the trunk T would obtain preference as the ground circuit for the E and F relays would extend over the back contact of the relay 16 and the relay E on energizing would open the initial energizing circuit of the relays E and F If, on the other hand, the last call had been made over-the trunk T and at the completion of said call other calls were waiting simultaneously on trunks T and T the relay 16 which is slightly slow acting would not be deenergized and the trunk T, would obtain preference, the circuit for its E and F relays extending from battery, over the front right hand contact of relay 15, back left hand contact of relay 1),, windings of relaysE and F back left hand contact of relay F back right hand contact of relayE front left hand contact of relay F through the winding of relay 16 to ground. The circuit for the relays E and 1? would pass over the back left hand contact of relay F back right hand contact of relay E back left hand 1 contact of relay F front contact of relay 16 and over the righthand contact of relay E Consequently, the relay 11, upon being energized would prevent the energization of the relays E and F Without describing the details of the circuit further, it will be apparent thatif an interval elapses between the last call and a plurality of simultaneous. calls made thereafter the order of preference will begin with the trunk T and pass over the trunks to the right thereof. If, however. no interval elapses between the last call and a plurality of simultaneously awaiting'calls, the first trunk to the right of the trunk on which the last call arose will obtain preference and the calls on the'remaining trunks will be taken up in regular order from left to right.

By means of the arrangements above dedescribed the operation of trunking calls be tween different offices is much simplified and the possibility of error in making connections is greatly reduced.

Furthermore, it will be obvious that the general principles herein disclosed may be .embodied in many other organizations lines terminating at said office, a plurality of trunks extending between said offices for extending connections from said lines and vover said link circuits to the other office, an

operators telephone set common to said trunks at the other ofiice, means responsive to the association of a link circuit with one of said trunks to automatically connect said telephone set with said trunk, and means to determine the order in which said set will be successively connected with a plurality of trunks with which a plurality of link circuits have been associated.

2. In a telephone system, two offices, subscribers lines terminating at each ofiice, a plurality of trunks extending between said ofiices, an operators set common to said trunks, means responsive to the establislr ment of a connection with one of said trunks to automatically connect said set thereto, and

means to determine the order in which said set will vbe successively connected with a plurality of trunks with which'connections have been established.

- 3. In a telephone system, two offices, link circuits at one of said offices, a plurality of trunks extending between said ofiices, an operators telephone set common to said trunks at the other oflice, means responsive to the association of a link circuit with one of said trunks to automatically connect said telephone set with said trunk, and means to antomatically vary the order in which said set will'be successively connected with a plurality of trunks with which a plurality of link circuits are associated. 7

4C. In a telephone system, two ofiices,-a plurality of trunks extending between said offices, an operators set common'to said trunks, means responsive to the establishment of a connection with one of said trunks to automatically connect said set thereto, and means to automatically vary the order in which said set will be successively connected with a plurality of trunks with which connections are established.

In a telephone system, two offices, link circuits at one of said offices, an operators set common to said link circuits, a plurality of trunks extending between said offices, an

' operators set common to said trunks at the other office, means responsive to the associa tion of a link circuit with one of said trunks to automatically connect said last mentioned'opera-tors set with said trunk, means to associate said first mentioned operators set with-said trunk to the exclusion of a calling subscriber associated therewith by means of a link circuit, and means to determine the circuits at one of said ofiices, an operators set common to said link circuits, a plurality of trunks extending between sa1d offices, an

operators set common to said trunks at the other otfice, means responsive to the association of a link circuit with one of said trunks to automatically connect said last mentioned. operators set with said trunk, means to as sociate said first mentioned operators set I with said trunk to the exclusion of a calling subscriber associated therewith by means of a link circuit, and means to vary the order in which the operators set common to said trunks will be successively connected to a plurality of trunks with which connections are established. I

7. In a telephone system, two ofiices, link circuits at one of said ofiices, a plurality of trunks extending between said'ofiices, an operators telephone set common to said trunks at the other oflice, means responsive to the association of a link circuit with one of said trunks to automatically connect said tel e phone set with said trunk, and means to cletermine-the order in which said set will be successively connected with a plurality of trunks with which a plurality of link circuits have been associated, said means being .so arranged that when link circuits have been associated with a plurality of trunks said operators set will be successively connected with said trunks in regular order, beginning with thetrunk next in order to the last trunk with which a link circuit had been previously connected. I y

8. In a telephone system, two oflices, a plurality of trunks extending between said offices, an operators set common to said trunks, means responsive to the establishment of a connection with one of said trunks to automatically connect said set thereto, and means to determine the order in which said set will be successively connected with a plurality of trunks with which connections have been established, said means being so arranged that when connections have been established with a plurality of trunks said operators set will be successively connected with said trunks in regular order, beginning with he trunk next in order to the last trunk with which a connection had been previously established.

n a telephone system, twooflices, a- I plurality of trunks extending between said ofiices, an operators set common to said trunks, a relay for each trunk responsive to the establishment of a connection with 1ts corresponding trunk to automatically connect said set thereto, and means controlled by said relays to determine the order in which said set wlll be successively connected with a plurality of trunks with which con-.

nections have been established.

10. In a telephone system, two oflices, a plurality of trunks extending between said OffiCGS, an operators set common to said trunks, a relay for each trunk responsive to the establishment of a connection with its corresponding trunk to automatically con- .nect said set thereto, and means controlled by said relays to vary the order in which said set will be successively connected with a plurality of trunks with which connections have been established.

11. In a telephone system, two otiices, a plurality of trunks extending between said otfices, an operators set common to said trunks, a relay for each trunk responsive to the establishment of a connection with its corresponding trunk to automatically connect said set thereto, the circuits of the relays being so arranged that with respect to any given relay the circuits of all ofthe other relays of the group pass through the contacts of said relay, whereby when the relay corresponding to one trunk is operated the circuits of the remaining relays of the group are held open.

12. In a telephonesystem, two oflices, link circuits at one of said 'oflices, a plurality of trunks extending between said offices, an operators telephone set common to said trunks at the other office, means responsive to the association of a link circuit with one of said trunks to automatically connect said telephone set with said trunk, means responsive to the connection of said, trunk to :1 called line to automatically disconnect said set from said trunk, and means controllable by the operator at will for disconnecting said set from said trunk while maintaining the set in operative condition for connection with another trunk.

13. In a telephone system, two oflices, link circuits at one of said oliices, a. plurality of trunks extending between said oiiices, an operators telephone set common to said trunks at the other oflice, means responsive to the association of a link circuit with one of said trunks to automatically connect said telephone set with said trunk, signals indi' vidual to each trunk to indicate the condition of a connection established over the trunk and means whereby when link circuits are associated with a plurality of trunks simultaneously a special signal will be given for the trunk with which the operators set is associated.

14. In a telephone system, two ottices, link circuits at one of said oftices, a plurality of trunks extending between said otiices, an operators telephone set common to said trunks at the other oflice, means responsive to the association ofa-Iink circuit with one of said trunks toautomatically connect said telephone set with sald trunk,'s1gnals individual to each trunk to indicate the condition of a connection established over the" trunk, means whereby when link circuits are associated with a plurality of trunks simultaneously a-special signal will be given for HENRY M. BA'SCOM. 

